; these are our constants needed by Grub
DS_MAGIC equ 3544DA2Ah
MULTIBOOT_PAGE_ALIGN equ 1<<0
MULTIBOOT_MEMORY_INFO equ 1<<1
MULTIBOOT_AOUT_KLUDGE equ 1<<16
MULTIBOOT_HEADER_MAGIC equ 0x1BADB002
MULTIBOOT_HEADER_FLAGS equ MULTIBOOT_PAGE_ALIGN | \
                           MULTIBOOT_MEMORY_INFO | \
                           MULTIBOOT_AOUT_KLUDGE
MULTIBOOT_CHECKSUM equ -(MULTIBOOT_HEADER_MAGIC \
                         +MULTIBOOT_HEADER_FLAGS)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; code section

SECTION .text
BITS 32

; extern symbols
EXTERN _stext, _sbss, _end
ALIGN 4

; needed by Grub too
mboot:
  dd MULTIBOOT_HEADER_MAGIC
  dd MULTIBOOT_HEADER_FLAGS
  dd MULTIBOOT_CHECKSUM
  dd mboot
  dd _stext
  dd _sbss
  dd _end
  dd entry

; our "main()" function for the assembly.
GLOBAL entry
entry:

  ; sanity check
  mov eax,[ds_magic]
  cmp eax,DS_MAGIC
  je ds_ok

  ; if we got here, there was a problem loading the kernel
  ; we put a 'E' and halt
  mov word [0B8000h], 0f45h
  jmp short $


ds_ok:
  ; if we got here, eveything's alright.
  EXTERN _sbss, _end

  ; zeroing the stack
  mov edi,_sbss
  mov ecx,_end
  sub ecx,edi
  xor eax,eax
  rep stosb

  ; setting the stack pointer
  mov esp,stack

  ; calling our kmain()
  extern kmain
  call kmain

  jmp $

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; data section

SECTION .data
ds_magic:
  dd DS_MAGIC


; This will set up the new segment registers. We need to do
; something special in order to set CS. We do what is called a
; far jump. A jump that includes a segment as well as an offset.
; This is declared in C as 'extern void _gdt_flush();'
global _gdt_flush     ; Allows the C code to link to this
extern gp            ; Says that '_gp' is in another file
_gdt_flush:
    lgdt [gp]        ; Load the GDT with our 'gp' which is a special pointer
    mov ax, 0x10      ; 0x10 is the offset in the GDT to our data segment
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    jmp 0x08:flush2   ; 0x08 is the offset to our code segment: Far jump!
flush2:
    ret               ; Returns back to the C code!


; Loads the IDT defined in '_idtp' into the processor.
; This is declared in C as 'extern void _idt_load();'
global _idt_load
extern idtp
_idt_load:
    lidt [idtp]
    ret
    
; Interrupt Service Routines (ISRs)
global _isr0
global _isr1
global _isr2
global _isr3
global _isr4
global _isr5
global _isr6
global _isr7
global _isr8
global _isr9
global _isr10
global _isr11
global _isr12
global _isr13
global _isr14
global _isr15
global _isr16
global _isr17
global _isr18
global _isr19
global _isr20
global _isr21
global _isr22
global _isr23
global _isr24
global _isr25
global _isr26
global _isr27
global _isr28
global _isr29
global _isr30
global _isr31

;  0: Divide By Zero Exception
_isr0:
    cli
    push byte 0
    push byte 0
    jmp isr_common_stub

;  1: Debug Exception
_isr1:
    cli
    push byte 0
    push byte 1
    jmp isr_common_stub

;  2: Non Maskable Interrupt Exception
_isr2:
    cli
    push byte 0
    push byte 2
    jmp isr_common_stub

;  3: Int 3 Exception
_isr3:
    cli
    push byte 0
    push byte 3
    jmp isr_common_stub

;  4: INTO Exception
_isr4:
    cli
    push byte 0
    push byte 4
    jmp isr_common_stub

;  5: Out of Bounds Exception
_isr5:
    cli
    push byte 0
    push byte 5
    jmp isr_common_stub

;  6: Invalid Opcode Exception
_isr6:
    cli
    push byte 0
    push byte 6
    jmp isr_common_stub

;  7: Coprocessor Not Available Exception
_isr7:
    cli
    push byte 0
    push byte 7
    jmp isr_common_stub

;  8: Double Fault Exception (With Error Code!)
_isr8:
    cli
    push byte 8
    jmp isr_common_stub

;  9: Coprocessor Segment Overrun Exception
_isr9:
    cli
    push byte 0
    push byte 9
    jmp isr_common_stub

; 10: Bad TSS Exception (With Error Code!)
_isr10:
    cli
    push byte 10
    jmp isr_common_stub

; 11: Segment Not Present Exception (With Error Code!)
_isr11:
    cli
    push byte 11
    jmp isr_common_stub

; 12: Stack Fault Exception (With Error Code!)
_isr12:
    cli
    push byte 12
    jmp isr_common_stub

; 13: General Protection Fault Exception (With Error Code!)
_isr13:
    cli
    push byte 13
    jmp isr_common_stub

; 14: Page Fault Exception (With Error Code!)
_isr14:
    cli
    push byte 14
    jmp isr_common_stub

; 15: Reserved Exception
_isr15:
    cli
    push byte 0
    push byte 15
    jmp isr_common_stub

; 16: Floating Point Exception
_isr16:
    cli
    push byte 0
    push byte 16
    jmp isr_common_stub

; 17: Alignment Check Exception
_isr17:
    cli
    push byte 0
    push byte 17
    jmp isr_common_stub

; 18: Machine Check Exception
_isr18:
    cli
    push byte 0
    push byte 18
    jmp isr_common_stub

; 19: Reserved
_isr19:
    cli
    push byte 0
    push byte 19
    jmp isr_common_stub

; 20: Reserved
_isr20:
    cli
    push byte 0
    push byte 20
    jmp isr_common_stub

; 21: Reserved
_isr21:
    cli
    push byte 0
    push byte 21
    jmp isr_common_stub

; 22: Reserved
_isr22:
    cli
    push byte 0
    push byte 22
    jmp isr_common_stub

; 23: Reserved
_isr23:
    cli
    push byte 0
    push byte 23
    jmp isr_common_stub

; 24: Reserved
_isr24:
    cli
    push byte 0
    push byte 24
    jmp isr_common_stub

; 25: Reserved
_isr25:
    cli
    push byte 0
    push byte 25
    jmp isr_common_stub

; 26: Reserved
_isr26:
    cli
    push byte 0
    push byte 26
    jmp isr_common_stub

; 27: Reserved
_isr27:
    cli
    push byte 0
    push byte 27
    jmp isr_common_stub

; 28: Reserved
_isr28:
    cli
    push byte 0
    push byte 28
    jmp isr_common_stub

; 29: Reserved
_isr29:
    cli
    push byte 0
    push byte 29
    jmp isr_common_stub

; 30: Reserved
_isr30:
    cli
    push byte 0
    push byte 30
    jmp isr_common_stub

; 31: Reserved
_isr31:
    cli
    push byte 0
    push byte 31
    jmp isr_common_stub


; We call a C function in here. We need to let the assembler know
; that '_fault_handler' exists in another file
extern _fault_handler

; This is our common ISR stub. It saves the processor state, sets
; up for kernel mode segments, calls the C-level fault handler,
; and finally restores the stack frame.
isr_common_stub:
    pusha
    push ds
    push es
    push fs
    push gs
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov eax, esp
    push eax
    mov eax, _fault_handler
    call eax
    pop eax
    pop gs
    pop fs
    pop es
    pop ds
    popa
    add esp, 8
    iret


global _irq0
global _irq1
global _irq2
global _irq3
global _irq4
global _irq5
global _irq6
global _irq7
global _irq8
global _irq9
global _irq10
global _irq11
global _irq12
global _irq13
global _irq14
global _irq15

; 32: IRQ0
_irq0:
    cli
    push byte 0
    push byte 32
    jmp irq_common_stub

; 33: IRQ1
_irq1:
    cli
    push byte 0
    push byte 33
    jmp irq_common_stub

; 34: IRQ2
_irq2:
    cli
    push byte 0
    push byte 34
    jmp irq_common_stub

; 35: IRQ3
_irq3:
    cli
    push byte 0
    push byte 35
    jmp irq_common_stub

; 36: IRQ4
_irq4:
    cli
    push byte 0
    push byte 36
    jmp irq_common_stub

; 37: IRQ5
_irq5:
    cli
    push byte 0
    push byte 37
    jmp irq_common_stub

; 38: IRQ6
_irq6:
    cli
    push byte 0
    push byte 38
    jmp irq_common_stub

; 39: IRQ7
_irq7:
    cli
    push byte 0
    push byte 39
    jmp irq_common_stub

; 40: IRQ8
_irq8:
    cli
    push byte 0
    push byte 40
    jmp irq_common_stub

; 41: IRQ9
_irq9:
    cli
    push byte 0
    push byte 41
    jmp irq_common_stub

; 42: IRQ10
_irq10:
    cli
    push byte 0
    push byte 42
    jmp irq_common_stub

; 43: IRQ11
_irq11:
    cli
    push byte 0
    push byte 43
    jmp irq_common_stub

; 44: IRQ12
_irq12:
    cli
    push byte 0
    push byte 44
    jmp irq_common_stub

; 45: IRQ13
_irq13:
    cli
    push byte 0
    push byte 45
    jmp irq_common_stub

; 46: IRQ14
_irq14:
    cli
    push byte 0
    push byte 46
    jmp irq_common_stub

; 47: IRQ15
_irq15:
    cli
    push byte 0
    push byte 47
    jmp irq_common_stub

extern _irq_handler

irq_common_stub:
    pusha
    push ds
    push es
    push fs
    push gs

    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov eax, esp

    push eax
    mov eax, _irq_handler
    call eax
    pop eax

    pop gs
    pop fs
    pop es
    pop ds
    popa
    add esp, 8
    iret


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; uninitialized data section (empty)
SECTION .bss
    resb 8192               ; This reserves 8KBytes of memory here

stack:
